A semiconductor device for detecting a physical quantity distribution has been used in various fields, the semiconductor device comprising a line or matrix array of a plurality of unit components (for example, pixels) sensitive to changes in physical quantities of electromagnetic waves such as light, radiation, or the like, which is input from the outside.
For example, in the field of picture devices, CCD (Charge Coupled Device), MOS (Metal Oxide Semiconductor), CMOS (Complementary Metal Oxide Semiconductor) solid-state image sensing devices are used for detecting changes in light (an example of electromagnetic waves) as an example of physical quantities. In these devices, a physical quantity distribution is converted to an electric signal by unit components (in a solid-state image sensing device, pixels) and is read as the electric signal.
For example, in a solid-state image sensing device, a photodiode serving as a photoelectric conversion element (light-receiving element: photosensor) and provided in an image sensing portion (pixel potion) of a device portion detects an electromagnetic wave such as light, radiation, or the like, which is input from the outside, to generate signal electric charge and store it, so that the stored signal electric charge (photoelectron) is read as image information.
In order to acquire a signal having color information by a single image sensing device, a conventional single-plate solid-state image sensing device for color images mainly comprises a color filter (color separating filter) provided on the light-receiving surface side of an imaging portion, for discriminating (separating) among colors.
In this case, an individual color component must be aligned to a photoelectric conversion element constituting each pixel, and the unit of color separation corresponds to the repetition period of the color separating filter.
Examples of color filter combination include a primary color system using the three colors including red (R), green (G), and blue (B), and a complementary color system using the four colors including yellow (Y), cyan (C), magenta (M), and green (G). The primary color system has higher color reproducibility than that of the complementary color system, but the complementary color system is advantageous in that a color filter has high transmittance to cause high sensitivity. In reproducing an image, color signals (for example, primary color signals of R, G, and B) obtained using the primary color-system or complementary color-system color filter are processed to synthesize a luminance signal and color-difference signal.
Any one of combinations of primary color- or complementary color-system color filters includes a subtractive color filter in which only a specified wavelength region component is transmitted and led to a photoelectric conversion element, and other wavelength region components are cut off for performing color selection.
For example, when a light-detecting semiconductor layer is provided as a photoelectric conversion element below each of subtractive color filters of the three primary colors, i.e., red, green, and blue, which are used for discriminating among colors, light of each of the primary colors transmitted through the respective subtractive color filters can be individually detected.
However, a subtractive color filter system has low efficiency of light utilization because a large quantity of light is cut off. In particular, when filters of the primary colors, i.e., red, green, and blue, are used for discriminating among the colors, the quantity of light is decreased to ⅓ or less.
Also, a photoelectric conversion element is required for each color, and thus at least tree photoelectric conversion elements are required for one unit of color separation, thereby causing difficulty in realizing a high-density pixel sensor. Furthermore, a color separating filter is required to increase cost.
In order to solvent the problems of such a subtractive color filter, a sensor has been recently proposed, in which colors are discriminated using changes in absorption coefficient of a semiconductor with light wavelengths.
FIG. 113 is a drawing illustrating the mechanism of the sensor. FIG. 113(A) is a drawing showing the light absorption spectral characteristics of a semiconductor layer, and FIG. 113(B) is a schematic drawing showing the sectional structure of a device.
In the mechanism, the absorption coefficient of a Si (silicon) semiconductor for the primary color lights decreases in the order of blue, green, and red, as shown by 113(A). Namely, for blue color light, green color light, and red color light contained in incident light L1, the position dependence in the depth direction according to wavelengths is utilized, and layers for detecting the blue, green, and red color lights are provided in that order from the surface of the Si semiconductor in the depth direction, as shown in FIG. 113(B).
However, in the mechanism which utilizes changes in absorption coefficient with wavelengths, the quantity of light which can be theoretically detected is not decreased, but red color light and blue color light are absorbed by the blue color light detecting layer to some extent when being passed therethrough, and are thus detected as blue color light. Therefore, even when there is originally no blue signal, a blue signal is generated by absorption of green light and red light to produce alias, thereby failing to achieve sufficient color reproducibility.
In order to avoid this problem, correction by computation signal processing must be required for all signals of the primary colors, and thus a circuit must be separately required for computation, thereby complicating and scaling-up the circuit configuration and increasing the cost. Furthermore, for example, when one of the primary colors is saturated, the original value of light of the saturated color cannot be determined to cause error in computation. As a result, a signal of the color is processed differently from the original color.
Also, as shown in FIG. 113(A), most of semiconductors have absorption sensitivity to infrared light. Therefore, for example, in a solid-state image sensing device (image sensor) using a Si semiconductor, an infrared cut filter must be provided as an example of subtractive filter in front of the sensor.
On the other hand, there have recently been demands for a single a solid-state image sensing device to simultaneously take a visible light image and an infrared light image. For example, an infrared luminous point is previously prepared so that an infrared luminous point in the visible image can be detected by tracing the previously prepared infrared luminous point. For example, in the night without visible light, a clear image can be obtained by imaging with infrared irradiation.
In order to receive infrared light as a signal to take an image, it is necessary to remove an infrared cut filter or decrease the ratio of the infrared light cut.
However, in this case, infrared light is mixed in visible light and incident on a photoelectric conversion element, thereby causing a difference between the color of a visible light image and the original color.
Apart from the above-described problem, visible light is cut to some extent by the infrared cut filter used in an ordinary solid-state image sensing device, and thus sensitivity is decreased. Also, the use of the infrared cut filter increases the cost.
The present invention has been achieved in consideration of the above situation, and an object of the invention is to provide a new semiconductor device capable of increasing (typically improving the conversion efficiency of light quantity) the quantity of electromagnetic waves (typically, quantity of light) incident per unit area (substantially a unit component such as a photoelectric conversion element) without using a subtractive color filter, a drive controlling technique and manufacturing method therefor, and a mechanism using the semiconductor device for acquiring physical information.
In an example, the invention provides a mechanism for an imaging technique capable of achieving high resolution and sufficient color reproducibility.
In another example, the invention provides a mechanism capable of simultaneously taking a visible light image with a correct color and an infrared or ultraviolet light image using a single semiconductor device.